Two interrelated models have been presented which describe 1) the regulation of surface growth of Streptococcus faecalis by chromosome replication; and 2) a shape-determining mechanism which directs the assembly of envelope precursors into new cell surface. The first model provides that during a round of chromosome synthesis a signal is produced which results in the formation of a surface growth site. This site, once formed, enlarges the cell surface until a second signal, produced during the terminal stages of chromosome replication, inhibits further enlargement and initiates septation. The second model is concerned with the actual construction and function of the surface growth point once it has been formed. This model suggests that surface growth originates from the assembly of wall precursors along the leading edge of the cross wall at a rate of R1. This synthesis is thought to create the equivalent of two parallel layers in the cross wall which subsequently peel apart into two layers of peripheral wall. The rate of layer separation, R2, proceeds at a relatively constant rate of layer separation, R2, and surface enlargment are inhibited and septal closure is stimulated. Methods have been devised which can compare the amount and thickness of the cell envelope in various portions of the cell with the macromolecular content and autolytic activity of cells of equivalent volumes. In attempting to test many aspects of the above models, these methods will be applied to steady-state, synchronous, and un-balanced populations where specific inhibition of DNA, RNA, protein, or wall biosynthesis has been induced. BIBLIOGRAPHIC REFERENCES: Tsien, H.C., Shockman, G.D. and Higgins, M.L. Structure and Molecular organization of the cell wall of Streptococcus faecalis. Bacteriol. Proc. 75:165, (1975). Shockman, G.D., Daneo-Moore, L., Higgins, M.L. and Hinks, R. On the role of autolytic enzyme activity in the regulation of the streptococcal surface growth and division cycle. Abstr. Lunteren Lectures on Molecular Genetics (1975).